Strap clamping and severing assembly for strapping tools

ABSTRACT

A strap clamping and severing assembly which cooperates with a movable sealing head of a strapping tool and performs the multiple functions of first clamping the free end of a length of strapping in a fixed position preparatory to creating a loop of the strapping about an article; secondly, of guiding the feed end of the loop during the tensioning operation in overlapped relation to the clamped free end; thirdly, of severing the feed end of the loop from the strapping source after the tensioning operation; and fourthly, of retaining the severed end of the strapping source in an accessible position to facilitate the next succeeding strapping operation. When used with a vibratory sealing head which effects a fusion joint on the loop overlap, the assembly vibrates in unison with the head and severs the strap directly at the edge of the sealing area to eliminate a protruding tail.

United States Patent Angarola [451 Mar. 14, 1972 STRAP CLAMPING AND SEVERING ASSEMBLY FOR STRAPPING TOOLS [72] Inventor: Barry R. Angarola, Schaumburg, Ill.

[73] Assignee: Signode Corporation, Chicago, Ill.

' [22] Filed: Apr. 1, 1970 [21] Appl. No.: 24,587

[52] US. 1Cl......' ..140/93.2, 140/1236 [51] Km. C1. ..B21f 9/02 [58] Field ofSearch ..140/93,93.2,93.4, 123.6; 156/73; 100/33 PB [56] References Cited UNITED STATES PATENTS 2,368,969 2/1945 Cleveland ..140/93.4

2,868,238 1/1959 Hall 140/93 2 3,396,760 8/ 1968 Kirsinas et al. 140/934 3,442,733 5/1969 Vilcins ..156/73 Primary Examiner-Lowell A. Larson AttorneyEdward R. Lowndes [5 7] ABSTRACT A strap clamping and severing assembly which cooperates with a movable sealing head of a strapping tool and performs the multiple functions of first clamping the free end of a length of strapping in a fixed position preparatory to creating a loop of the strapping about an article; secondly, of guiding the feed end of the loop during the tensioning operation in overlapped relation to the clamped free end; thirdly, of severing the feed end of the loop from the strapping source after the tensioning operation; and fourthly, of retaining the severed end of the strapping source in an accessible position to facilitate the next succeeding strapping operation. When used with a vibratory sealing head which elfects a fusion joint on the loop overlap, the assembly vibrates in unison with the head and severs the strap directly at the edge of the sealing area to eliminate a protruding tail.

10 Claims, 6 Drawing Figures PATENIEDMAR 14 m2 SHEET 2 0F 2 I I 28 I m a ,w l/E/VTOR BARRY R. A/VGAROLA 1 s4 78 4s 48 I4 22 STRAP CLAMPING AND SEVERING ASSEMBLY FOR STRAIPING TOOLS The strap clamping and severing assembly of the present invention has been designed for use in connection with strap tensioning and sealing tools of the general type shown and described in a copending application, Ser. No. 24,667, filed of even date herewith, and entitled Strap Tensioning and Sealing Tool," and of which application the present one is a division.

The strapping tool of the aforementioned copending application is adapted to operate upon the overlapping end regions of a loop of thermoplastic strapping which has been caused to encircle an article,'the tool functioning first to tension the strapping loop about the article, secondly to sever the feed end of the strapping loop from the source of strapping, and thirdly to effect interfacial rubbing of the overlapping regions of the tensioned loop, one against the other, to develop a degree of friction-inducted heat sufficient to fuse the interfacial contacting surfaces and cause them to blend together so that, after the friction-producing operation has been terminated, solidification takes place and a weld or joint is produced. Although the strap clamping and severing assembly of the present application has been shown and described, both in the aforementioned copending application and in the present application, as being operatively associated with a strapping tool of the friction induced fusion welding type, the present strap clamping and severing assembly is not necessarily limited to such use and the same may, if desired, with or without modification as required, be employed in connection with strapping tools in which the strap sealing operation is carried out by means other than strap fusion means, as for example by crimping a metal seal about the strap loop overlap. Irrespective however of the particular use to which the present strap clamp and severing assembly may be put, the essential features thereof are at all times preserved.

Briefly, the strap clamping and severing assembly of the present invention, when operatively associated with a strapping tool, is mounted onand movable bodily with the vertically movable sealing head which invariably forms a functional element of the tool. The assembly includes a normally retracted spring biased cutter latch or block which functions automatically in connection with the normal operation of the tool to facilitate loading of the tool with strapping in that when manually released it serves to anchor the free end of the strapping so that the operator may pass the strapping around the article and thus establish the strapping loop. After the loop has been formed, a ball detent holds the feed end of the strapping loop in its overlapping relation with respect to the anchored feed end thereof. Upon commencement of the tool cycle, during the initial tensioning portion thereof, the ball detent permits slippage of the feed end of the loop overlap therebeneath until the desired degree of tension is attained. Thereafter, as the sealing head descends to create the seal or joint at the overlap, a cutting edge on the sealing head cooperates with a cutting edge on the cutter block to free the tensioned loop from the strapping source. Sealing thus takes place after the loop has been severed from the strapping source and, when it has been completed, the sealing head is raised and restored to its original position to release the sealed loop overlap so that the strapped article may be withdrawn from the tool, while at the same time the return movement of the sealing head also returns the cutter assembly to its original retracted position preparatory to the next succeeding tool cycle. The present strap clamping and severing assembly functions entirely in a mechanical manner under the control of the movements of the sealing head, whether the latter is power actuated as in the case of an air operated tool, or mechanically operated as in the case of a hand tool.

The aforementioned function of the strap clamping and severing assembly take place whether the assembly be used with a descending sealing head having seal-crimping jaws or a pressure jaw head of the vibratory type. When used with a vibrating sealing head, the cutter assembly vibrates in unison therewith so that there will be no separation of the cutter edges at the precise moment of shear and thus, shearing of the protruding portion of the strapping takes place at a point substantially contiguous to the sealed area with no strap residue or tail" remaining on the joint.

In the accompanying two sheets of drawings forming a part of this specification, one exemplary form of a strap clamping and severing assembly embodying the principles of the invention has been illustrated in connection with a strapping tool of the general type shown in the above-mentioned copending application, Ser. No. 24,667.

In these drawings:

FIG. I is a rear elevational view of an air operated strapping tool embodying the strap clamping and severing assembly of the present invention;

FIG. 2 is a fragmentary perspective view of the strap overlap joint which is effected by the tool of FIG. ll;

FIG. 3 is an enlarged exploded perspective view of the strap clamping and severing assembly, showing the same operatively associated with the sealing head of the strapping tool of FIG. 1;

FIG. 4 is a fragmentary side elevational view, partly in section and with certain parts removed, showing the tool in its normal air-applied condition and illustrating the position of the strap clamping and severing assembly at the commencement of the strap loading operation;

FIG. 5 is a fragmentary side elevational view, similar to FIG. 4, and illustrating the position of the strap clamping and severing assembly after the strap loading operation has been completed;

FIG. 6 is a fragmentary side elevational view, similar to FIG. 4 and 5, and illustrating the position of the strap clamping and severing assembly after the feed end of the strapping has been severed from the tensioned strapping loop and the sealing operation has commenced.

Referring now to the drawings in detail and in particular to FIG. 11, the strap clamping and severing mechanism of the present invention has been designated in its entirety at 10 and it is shown as being operatively applied to a pneumatically operable strapping tool 12 of the type shown and described in the aforementioned copending application, Ser. No. 24,667. The assembly 10 is dependent for its operation upon the operation of the tool 12, and particularly upon the movements of a jaw supporting vibratory sealer block 14 associated with a strap sealing head 15 (see also FIG. 3) and therefore, in order to facilitate an understanding of the assembly 10 and its operation, it is necessary that at least the strap loading, strap tensioning, strap severing and strap sealing functions of the tool 12 be understood. Accordingly, in the accompanying drawings only those portions of the tool 12 which are considered essential to such tool functions have been illustrated.

' For a more complete understanding of the nature and operation of the tool 12, reference may be had to such copending application, the entire disclosure of which, insofar as it is consistent with the present disclosure, is hereby incorporated in and made a part of this application by reference thereto.

Briefly, the strapping tool 12 is designed to tension a loopof thermoplastic strapping material such as Nylon, polypropylene or other fusible material about an article and, thereafter, when the desired degree of tension in the loop has been attained, effect a joint between the overlapping portions of the loop by creating a fusion weld between the abutting interfacial surfaces of such overlapping portions. Accordingly, the tool includes a composite casing 16 (FIG. 1) which encloses the operative strapping instrumentalities and from which there projects downwardly a tool base 18 which is adapted to be supported upon an article undergoing strapping. Accordingly, in FIG. 5 the tool is shown as being seated upon an article A which is to be strapped, the not yet tensioned loop of the strapping S being considered to encircle the article and being operatively loaded into the tool. The overlapping portions of the loop (which hereinafter will be referred to simply as the overlap) include a lower free end region L (see also FIG. 2) and an upper feed end region U, the latter extending from a suitable source of strapping as for example a dispensing reel (not shown).

Within the casing 16 there are disposed a strap tensioning assembly 20 (FIG. 4) including a feed wheel 22 and its associated gripper foot 24: a strap sealing or joint-forming assembly 26 including the aforementioned sealing head (FIG. 3), a crank 28 for shifting the position of the sealing head, and an air cylinder 30 having a piston 32 operatively connected to the crank 28; and an air motor M (FIG. 1) which is housed within an extension 33 of the casing 16 and is operatively connected in driving relationship to both the tensioning assembly and the joint-forming assembly 26.

The specific construction of the tensioning assembly 20 forms no part of the present invention, it being deemed sufficient to state that a spring 34 (FIG. 4) yieldingly biases the gripper foot 24 to a position wherein it cooperates with the feed wheel 22 for strap-impelling purposes, and that normally a latch device 35 holds the gripper foot in an inoperative position remote from the feed wheel. Upon depression of a start button 36 (FIGS. 1 and 4) a plunger 38 engages the latch device 35 and releases the gripper foot 24, thus allowing the same to move into cooperation with the feed wheel 22.

At the time the start button 36 is depressed, certain pneumatic control devices are actuated and air is supplied to the motor M, and also to the lower end of the cylinder 30, thus maintaining the piston 32 in its uppermost position until such time as the desired degree of tension in the strapping loop is attained, at which time the supply of air to the cylinder is reversed, thus driving the piston 32 downwardly and actuating the crank 28 so as to initiate the sealing portion of the tool cycle in the manner set forth in the above-mentioned copending application, Ser. No. 24,667 and as will be described with some particularity herein presently.

The pneumatic control instrumentalities by means of which air is supplied to the cylinder 30 for actuating the joint-forming assembly 26 have not been illustrated or described herein since they constitute no part of the present invention. Neither have the gear trains leading from the motor M which supplies power for rotating the feed wheel 22 and for vibrating the sealer block 14 associated with the sealing head 15. It is deemed sufficient to state that the motor is connected by a first train of gearing to a feed wheel shaft 40 on which the feed wheel 22 is mounted, and is also connected by a second train of gearing to an eccentric shaft 42 by means of which rapid, small-amplitude vibration is continuously imparted to the sealer block 14 for friction fusion purposes as will be described presently.

The constantly vibrating sealer block 14 is vertically shiftable in the tool casing and the undemeath side thereof is provided with a series of gripperteeth which establish an upper sealing jaw 46. A similar series of gripper teeth on the upper surface of the tool base 18 establishes a cooperating lower sealing jaw 48. In the raised position of the sealer block as shown in FIGS. 4 and 5, the two sealing jaws 46 and 48 remain separated for reception of the strapping therebetween. In the lower position of the sealer block 14 as shown in FIG. 6, the strapping which has been inserted between the two jaws is operated upon thereby for sealing purposes by reason of the vibrational movement of the upper sealing jaw 46.

Vibrational movements are imparted to the sealer block 14 by means of a rapidly oscillating bushing 50 which is eccentrically disposed with respect to the shaft 42 and which operates in a vertical slot 52 formed in the sealer block 14. The bushing 50 is continuously oscillatable so that the sealer block 14 is continuously vibrated, idle vibration taking place during the early tensioning portion of the tool cycle while the sealer block is raised, and effective sealing vibration taking place during the sealing portion of the tool cycle when the block is lowered. v

The constantly reciprocating sealer block [4 is normally maintained in its raised position as shown in FIG. 4 under the influence of an upwardly biased pressure pad 53 (FIG. 3) which is in the form of an inverted channel member having depending flanges 54 and which seats upon the sealer block in saddle fashion. Pin and slot connections 56 between the flanges 54 and sides of the block 44 allow for lateral reciprocation of the block, as well as establishing a vertical thrust connection whereby the sealer block is yieldingly biased upwardly toward its raised position under the influence of a pair of compression springs 58 which are interposed between one of the flanges 54 and a fixed ledge or shelf 60 provided on the tool casing. Antifriction rollers 62, seated in grooves 64 in the upper face of the block 44 ride on the underneath side of the pad during oscillation of the block.

During the sealing portion of the tool cycle, downward pressure is applied to the pressure pad 53 and sealer block 14 by the piston 32 which operates, through a ram 66, on the crank 28 which carries a roller 67 that bears against a pressure plate 68 (see also-FIG. 3). A series of Belleville type spring washers 69 are interposed between the plate 70 and pressure pad 53 for transmitting the downward thrust of the former to the latter and consequently to the sealer block 14.

Considering now the strap clamping and severing assembly 10 of the present invention, this assembly includes a cutter block proper 70 in the form of a machined part or casting which is vertically movable in a recess or guideway 72 (FIG. 3) which is established by reason of a depending leg 74 provided on the sealer block 14 and which is spaced from the adjacent end face of the latter. The cutter block 70'is provided with a slot 76 in one side thereof for reception therein of the upper strap overlap U at the time the strap is loaded into the tool as shown in FIG. 5. The slot 76 defines a laterally projecting pressure foot 78, the underneath side of which is designed for cooperation with the fixed tool base 18 in clamping the lower strap overlap L in position in the tool after the strap loading operation has been completed. A spring 80 yieldingly urges the cutter block 70 downwardly to establish the necessary holding pressure against the base 18, the spring bearing at its upper end against an underneath surface of the sealer block 14 within the recess or guideway 72.

The slot 76 is designed to receive therein the upper strap overlap U at the time the strapping loop is undergoing manual formation and the tool is being loaded. To hold this upper overlap U, the cutter block 70 is formed with a vertical bore 82 therein and a detent ball 84 is floatingly disposed within this bore and is spring biased downwardly by means of a small diameter spring 86 which passes through the spring 80 and bore 82 and bears at its upper end against the aforementioned underneath surface on the sealer block 14. The detent ball thus exerts a light pressure on the upper strap overlap U and holds it in position during strap tensioning when the strap slides forwardly on the upper face of the pressure foot 78 and is guided in its sliding movement by a raised shoulder 88 on the pressure foot. It further functions to capture the excess strapping which is cut from the loop after the tensioning operation has been completed as will become clear when the operation of the cutter assembly 10 in conjunction with the operation of the tool 12 is set forth.

Normally, the cutter block 70 is held in a raised position relative to the sealer block 14 by means of a latch release element 90 which is bifurcated to provide a pair of latch fingers 92 which project beneath a pair of latch shoulders 94 defined by a pair of slots 96 in the cutter block 70. The latch release element 90 is pivoted on a pin 98 mounted on the depending leg 74 and is spring biased as indicated at 99. The latch release element 90 thus moves bodily and vertically in unison with the sealer block 14. During relative vertical movement between the sealer block 14 and the cutter block 70, a shearing edge 100 on the foot 78 cooperates with a shearing edge 102 on the sealer block to sever the tensioned strapping loop from the strapping source as illustrated in FIG. 6, thus leaving the free end of the strapping captured as previously stated.

The above described strap clamping and severing assembly 10 is directly related to the initial loading of the strapping into the tool. As shown in FIG. 4, in the normal position of the tool, after air has been supplied thereto, the latch release element 90 maintains the cutter block '70 in its raised position with respect to the sealer block M (which also is in its raised position) so that the free end region of the strapping may be slid sidewise between the feed wheel 22 and the gripper foot 24 which, at that time, remain separated. This free end region also is slid sidewise over the tool base I8 and beneath the pressure foot 7% on the cutter block 70. At this point the latch release element 90 is manually operated to release the cutter block 70 and allow it to move downwardly relative to the sealer block I4 as shown in FIG. 5 for clamping engagement with such free end region which subsequently becomes the lower strap overlap L. The strapping is then passed around the article A and is slid sidewise between the ball detent M and pressure foot 78 where it becomes frictionally captured, thereby establishing an untensioned strap loop having upper and lower overlap portions U and L and which subsequently becomes tensioned and thus shrunk upon the article as soon as the gripper foot 24 is brought into effective engagement with the rotating feed wheel 22 incident to depression of the start button 36 and consequent commencement of the tensioning cycle.

It is to be noted at this point that when the cutter block 70 is initially released by depression of the latch release element 90, the cutter latch comes to rest on the lower strap overlap L in such a position that the two latch fingers 92 now overlie the upper end of the cutter block 70 as shown in FIG. 5, the vibrating sealer block M at this time remaining in its raised position.

With the strapping tool 12 thus loaded with strapping and the strapping loop encircling the article A as shown in FIG. 5, depression of the start button 36 supplies air to the motor M as previously described to commence the rotation of the feed wheel and to initiate immediate vibration of the sealer block 14 and the entire cutter assembly carried thereby. Depression of the start button also releases the gripper foot 24l as previously described so that the strap overlaps U and L are then operated upon in the usual manner of feed wheel operation to tension the strapping loop. It should be borne in mind that during this tensioning operation the sealer block and cutter assembly are vibrating in unison but without function because the sealer block is in its raised position.

At such time as a predetermined degree of tension in the strapping loop has been attained, the reaction force on the motor causes the latter to approach a condition of stall, thereby building backup pressure in the motor feed line. This pressure is sensed and utilized to actuate the air cylinder and plunger assembly 30, 66 (FIG. 4) thereby driving the now vibrating sealer block I4 downwardly and into effective sealing engagement with the strap overlap. It is at this point in the tool cycle that the strap severing operation takes place.

In connection with such strap severing operation, it is to be noted that as shown in FIG. 6, the cutter block '70 is in its lowered position with the pressure foot 78 resting on the lower strap overlap L and with the latch fingers 92 underlying the shoulders 94. This is the lowermost position of which the cutter block is capable of assuming. Therefore, during downward movement of the vibrating sealer block M, the latter moves relative to the cutter block 70 so that the latch fingers 92 trip over the now immovable shoulders 94 and come to rest beneath these shoulders as shown in FIG. 6. At the same time, the shearing edge 1102 on the sealer block I4 moves downwardly past the shearing edge MN) on the cutter block 70, thus severing the protruding portion of the upper strap overlap U which has been pushed forwardly beyond the overlap during the tensioning operation. Although the sealer block M and cutter block 70 are both vibrating at the time of strap cutoff, these members are vibrating in unison so that no relative lateral displacement of the shearing edge takes place which might, otherwise, impair the sealing function.

Because there is no displacement between these shearing edges at the precise moment of shear, close shearing of the protruding portion of the strap overlap U takes place at a region of contiguity with respect to the sealed area and there is no strap residue or tail on the sealedjoint.

The phenomena by means of which heat of fusion takes place so that the interfacial regions of the strap overlap become blended to produce a joint has been set forth in the aforementioned copending application, Ser. No. 24,667 and need not be discussed herein. It is deemed sufficient to state that after a predetermined length of time the supply of air to the cylinder 30 is reversed so as to cause raising of the sealer block M. During such upward movement of the block, the depending leg 7l (FIG. 6) and the pin 93 carried thereby raises the latch release element while the latch fingers 92 act on the shoulders 94 and thus cause the cutter block 70 to move upwardly bodily with the sealer block so that the parts assume their initial positions as shown in FIG. 4 preparatory to the next succeeding strapping operation. Such upward movement of the sealer block and cutter block releases the completed overlap joint, as well as the lower strap overlap L for removal from the tool, while the ball detent 84L continues to hold the free end of the strapping source in a conveniently accessible position where it may be manually engaged by the operator during the next tool loading operation.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

I. In a strapping tool for uniting the inner and outer overlapping end portions of a tensioned loop of strapping which encircles an article, in combination, a tool base engageable with the article and over which said end portions extend, a sealing head movable vertically toward and away from said base between a raised inoperative position and a lowered position wherein it is effective to unite said end portions, a cutter block movable on said head between an upper position remote from the base to permit loading of the inner loop overlap therebetween and a lowered position wherein it clamps said inner overlap against the base, means yieldingly biasing said cutter block downwardly, manually releasable means normally maintaining the cutter block in its upper position, and cooperating strap severing edges on the cutter block and sealing head for shearing the excess strapping which projects from the outer loop overlap when the sealing head moves to its lowered position.

2. In a strapping tool, the combination set forth in claim 1, wherein said cutter block is provided with a laterally extending pressure pad adjacent its lower end and over which the outer loop overlap is adapted to extend, and yieldable detent means effective against said pressure pad for lightly clamping said outer loop overlap thereagainst while allowing for sliding movement of said latter overlap thereover.

3. In a strapping tool, the combination set forth in claim I, wherein said cutter block is provided with a guide slot therethrough for sliding reception of the outer loop overlap.

4. In a strapping tool for effecting interfacial fusion between the inner and outer overlapping end portion of a tensioned loop of thermoplastic strapping which encircles an article, a tool base engageable with the article and over which the overlapping end portions extend, a vibratory sealing head movable vertically toward and away from said base between a raised inoperative position and a lowered position wherein it is effective to engage said outer end portion and produce multidirectional frictional sliding movement thereof on the inner end portion with consequent interfacial fusion therebetween, a cutter block movably mounted on said sealing head for consequent vibration in unison therewith, said cutter block being movable bodily between an upper position remote from the base to permit loading of said inner end portion therebetween and a lowered position wherein it clamps said inner end portion against the foot, means yieldingly biasing the cutter block downwardly, manually releasable means normally maintaining the cutter block in its upper position, and cooperating strap shearing edges on the cutter block and sealing head for shearing the excess strapping which projects from the upper overlapping end portion when the vibrating sealing head moves to its lowered position.

5. In a strapping tool for tensioning a loop of strapping having inner and outer end portions establishing loop overlaps about an article, severing the excess strapping which projects from the outer end portion, and uniting said end portions to produce a seal at the overlap, tensioning mechanism engageable with the overlap for progressively applying tension to the loop and maintaining such tension, sealing mechanism including a fixed lower jaw member and an upper jaw member movable between a raised position removed from the lower jaw member to permit loading of the loop overlap therebetween, and a lowered position wherein it compresses the interposed'overlap against the lower jaw member for sealing purposes, a cutter block vertically slidable on said upper jaw member and having a lateral pressure foot adjacent its lower end, said block being movable between an upper position wherein said foot is raised from the lower jaw member to permit loading of the inner end portion therebetween and a lower position wherein the foot engages and clamps said inner end portion against the lower jaw member, means yieldingly biasing said cutter block downwardly, said pressure foot being adapted for reception of the outer end portion thereover in sliding relationship, means for moving said upper jaw member between its raised and its lowered positions, and cooperating strap severing edges on said pressure foot and upper jaw member and effective to shear the excess strapping which projects from the outer end portion at such time as the upper jaw member moves from its raised to its lowered position.

6. In a strapping tool, the combination set forth in claim and including, additionally, yieldable detent means effective against said pressure foot for lightly clamping said outer end portion thereagainst while allowing for sliding movement of said latter end portion thereover.

7. In a strapping tool, the combination set forth in claim 6 wherein said detent means comprises a detent ball engageable with said outer end portion and spring means yieldingly biasing said ball against said latter end portion.

8. In a strapping tool, the combination set forth in claim 7, wherein the biasing means for the cutter block comprises a compression spring interposed between the cutter block and upper jaw member.

9. In a strapping tool, the combination set forth in claim 7, wherein said pressure foot is established by the provision of a horizontal slot which is formed in one side of the cutter block,

'the cutter block is formed with a vertical bore therein communicating with the upper side of the slot, the detent means comprises a detent ball floatingly confined in the bore and a compression spring likewise confined in said bore and effective between the upper jaw member and ball to bias the ball downwardly toward said pressure foot, and the biasing means for the cutter block comprises a second compression spring surrounding the first spring and bearing at its ends against said upper jaw member and the rim region of said bore.

10. In a strapping tool, the combination set forth in claim 5 and including, additionally, an edge guide shoulder for the outer end portion on the upper surface of said pressure foot. 

1. In a strapping tool for uniting the inner and outer overlapping end portions of a tensioned loop of strapping which encircles an article, in combination, a tool base engageable with the article and over which said end portions extend, a sealing head movable vertically toward and away from said base between a raised inoperative position and a lowered position wherein it is effective to unite said end portions, a cutter block movable on said head between an upper position remote from the base to permit loading of the inner loop overlap therebetween and a lowered position wherein it clamps said inner overlap against the base, means yieldingly biasing said cutter block downwardly, manually releasable means normally maintaining the cutter block in its upper position, and cooperating strap severing edges on the cutter block and sealing head for shearing the excess strapping which projects from the outer loop overlap when the sealing head moves to its lowered position.
 2. In a strapping tool, the combination set forth in claim 1, wherein said cutter block is provided with a laterally extending pressure pad adjacent its lower end and over which the outer loop overlap is adapted to extend, and yieldable detent means effective against said pressure pad for lightly clamping said outer loop overlap thereagainst while allowing for sliding movement of said latter overlap thereover.
 3. In a strapping tool, the combination set forth in claim 1, wherein said cutter block is provided with a guide slot therethrough for sliding reception of the outer loop overlap.
 4. In a strapping tool for effecting interfacial fusion between the inner and outer overlapping end portion of a tensioned loop of thermoplastic strapping which encircles an article, a tool base engageable with the article and over which the overlapping end portions extend, a vibratory sealing head movable vertically toward and away from said base between a raised inoperative position and a lowered position wherein it is effective to engage said outer end portion and produce multidirectional frictional sliding movement thereof on the inner end portion with consequent interfacial fusion therebetween, a cutter block movably mounted on said sealing head for consequent vibration in unison therewith, said cutter block being movable bodily between an upper position remote from the base to permit loading of said inner end portion therebetween and a lowered position wherein it clamps said inner end portion against the foot, means yieldingly biasing the cutter block downwardly, manually releasable means normally maintaining the cutter block in its upper position, and cooperating strap shearing edges on the cutter block and sealing head for shearing the excess strapping which projects from the upper overlapping end portion when the vibrating sealing head moves to its lowered position.
 5. In a strapping tool for tensioning a loop of strapping having inner and outer end portions establishing loop overlaps about an article, severing the excess strapping which projects from the outer end portion, and uniting said end portions to produce a seal at the overlap, tensioning mechanism engageable with the overlap for progressively applying tension to the loop and maintaining such tension, sealing mechanism including a fixed lower jaw member and an upper jaw member movable between a raised position removed from the lower jaw member to permit loading of the loop overlap therebetween, and a lowered position wherein it compresses the interposed overlap against the lower jaw member for sealing purposes, a cutter block vertically slidable on said upper jaw member and having a lateral pressure foot adjacent its lower end, said block being movable between an upper posiTion wherein said foot is raised from the lower jaw member to permit loading of the inner end portion therebetween and a lower position wherein the foot engages and clamps said inner end portion against the lower jaw member, means yieldingly biasing said cutter block downwardly, said pressure foot being adapted for reception of the outer end portion thereover in sliding relationship, means for moving said upper jaw member between its raised and its lowered positions, and cooperating strap severing edges on said pressure foot and upper jaw member and effective to shear the excess strapping which projects from the outer end portion at such time as the upper jaw member moves from its raised to its lowered position.
 6. In a strapping tool, the combination set forth in claim 5 and including, additionally, yieldable detent means effective against said pressure foot for lightly clamping said outer end portion thereagainst while allowing for sliding movement of said latter end portion thereover.
 7. In a strapping tool, the combination set forth in claim 6 wherein said detent means comprises a detent ball engageable with said outer end portion and spring means yieldingly biasing said ball against said latter end portion.
 8. In a strapping tool, the combination set forth in claim 7, wherein the biasing means for the cutter block comprises a compression spring interposed between the cutter block and upper jaw member.
 9. In a strapping tool, the combination set forth in claim 7, wherein said pressure foot is established by the provision of a horizontal slot which is formed in one side of the cutter block, the cutter block is formed with a vertical bore therein communicating with the upper side of the slot, the detent means comprises a detent ball floatingly confined in the bore and a compression spring likewise confined in said bore and effective between the upper jaw member and ball to bias the ball downwardly toward said pressure foot, and the biasing means for the cutter block comprises a second compression spring surrounding the first spring and bearing at its ends against said upper jaw member and the rim region of said bore.
 10. In a strapping tool, the combination set forth in claim 5 and including, additionally, an edge guide shoulder for the outer end portion on the upper surface of said pressure foot. 